This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-188879 filed on Jun. 23, 2000.
1. Field of the Invention
The present invention relates to a valve timing adjusting device for changing valve opening-closing timing suitable for use in intake and exhaust valves of an internal combustion engine.
2. Description of the Prior Art
As a conventional valve timing adjusting device, there is a well known vane-type device in which a camshaft is driven through a timing pulley, a chain sprocket, etc. which turn synchronously with an engine crankshaft. The valve timing of at least any one of an intake valve and an exhaust valve is hydraulically controlled by a phase difference of relative rotation of the timing pulley, the chain sprocket, and the camshaft. Engine output and fuel consumption ratio are improved by adjusting the phase difference between the crankshaft and the camshaft to an optimum value in accordance with engine operating state.
In such a vane-type valve timing adjusting device using operation oil, when at least any one of the intake valve and the exhaust valve is actuated, the camshaft receives a load torque which varies between positive and negative loads. Therefore, when the operation oil is not sufficiently supplied during cranking of the engine, there might arise such a problem that a vane member oscillates with respect to a housing member containing the vane member, thereby hitting against the housing member to produce knocks. Here, the positive load torque is applied in the retarding direction of the camshaft with respect to the crankshaft, and the negative load torque is added in the advancing direction of the camshaft with respect to the crankshaft.
When operation fluid is not sufficiently supplied to the valve timing adjusting apparatus, a stopper piston included in a vane member is fitted into a fitting hole formed in a housing member to prevent a swing motion of the vane member against the housing member, thereby preventing the occurrence of the noise. When the operation fluid is supplied sufficiently, the stopper piston comes out of the housing member by the fluid pressure, so that a relative rotation of the vane member is controlled with respect to the housing member. The position at which the stopper piston is fitted into the fitting hole may be either a most retard or most advance position of the vane member with respect to the housing member or an intermediate position between the most retard and most advance positions.
However, when the stopper piston is fitted into the fitting hole during the relative rotation control, the relative rotation control is not executed. For avoiding such an inconvenience, a damper chamber is provided on an outer periphery of the stopper piston, thereby decreasing the speed of movement of the stopper piston toward the fitting hole.
When the engine is stopped, the stopper piston is desired to be fitted into the fitting hole promptly. However, when the damper chamber is hermetically sealed, a damping action exerts even when the stopper piston has reached a position where the stopper piston is fitted into the fitting hole, so that the moving speed of the stopper piston decreases and the stopper piston does not promptly fit in the fitting hole. For example, in a configuration wherein the stopper fin is fitted into the fitting hole at an advance side with respect to the most retard position, the stopper pin might pass over the fitting hole without being fitted therein due to the action of a load torque acting on the retard side.
A first object of the present invention is to provide a valve timing adjusting device which restrains a relative rotation of a driven-side rotor with respect to a driving-side rotor when an engine is stopped.
A second object of the present invention is to provide a valve timing adjusting device which prevents the relative rotation of the driven-side rotor with respect to the driving rotor from being restrained when the engine operates normally.
According to a first aspect of the present invention, a valve timing adjusting device includes a changeover means which causes a damper chamber to be opened when a driven-side rotor is positioned at an advance side over a predetermined angle position of a contacting portion with respect to a driving-side rotor and which causes the damper chamber to be sealed hermetically when the driven-side rotor is positioned at the predetermined angle position or at retard side over the predetermined angle position with respect to the driving-side rotor.
When the contacting portion is positioned at the predetermined angle position, the damper chamber is sealed hermetically and the speed of movement of the contacting portion in its contacting direction decreases. Thus, when the engine normally operates, the contacting portion does not contact the contacted portion even when a fluid pressure which the contacting portion receives in a contact-canceling direction at the contacting position changes, thereby preventing a relative rotation of the driven-side rotor with respect to the driving-side rotor from being restrained.
When the engine is stopped, if the driven-side rotor is positioned at an advance side over the predetermined angle position with respect to the driving-side rotor, the damper chamber is opened. Then, upon turning OFF of the engine, the fluid pressure applied to the contacting portion in the contact-canceling direction drops. Therefore, when the driven-side rotor rotates to the retard side toward the predetermined angle position due to a load torque which is applied until the engine stop, the contacting portion contacts the contacted portion. Thus, a relative rotation of the driven-side rotor with respect to the driving-side rotor is restrained when the engine starts.
According to a second aspect of the present invention, fluid chambers facing a contacting portion are all opened except a damper chamber. Thus, the other fluid chambers than the damper chamber do not act as damper chambers. Therefore, when the engine is stopped, the contacting portion contacts the contacted portion when the driven-side rotor reaches the predetermined angle position, thereby restraining a relative rotation of the driven-side rotor with respect to the driving-side rotor.